Cygnus X-1

Proper names: Cygnus X-1, V1357 Cygni
Catalog numbers:
     Henry Draper Extension (HDE) 226868, Bonner Durchmusterung (BD) +34°3815, Smithsonian Astrophysical Observatory (SAO) 69181, Hipparcos Input Catalog (HIC) 98298
Arity: binary
Points of interest:
     No anthology of popular science-fiction stars would be complete without the first suspected black hole to be discovered. The name Cygnus X-1 properly only refers to the B star of this pair, as it's the X-ray source. The "diameter" of Cygnus X-1 reported below is actually twice its Schwarzchild Radius, the distance from the center of a black hole at which its escape velocity equals the speed of light (also called the Event Horizon).
     The less interesting A star is a rotating ellipsoidal variable, perhaps in part due to its close proximity to its small-but-massive companion.

Right Ascension and Declination: 19h58m21.7s, +35°12'5.82" (epoch 2000.0)
Distance from Sol: 7200 light-years (2207 parsecs)
Standard error in distance: 11%
Source for distance: Burnham's Celestial Handbook
Celestial (X,Y,Z) coordinates in ly: 2905, -5116, 4150
Galactic (X,Y,Z) coordinates in ly: 2263, 6826, 353
Proper motion: 0.0071 arcsec/yr (135.0° from north)
Radial Velocity: -13 km/sec
Source for proper motion and radial velocity: Hipparcos Input Catalog
Galactic (U,V,W) velocity components in km/s: 13, -14, -73

What do all these fields mean?

Data for A and B's orbit around one other:
Period: 5.59982 days
Semimajor Axis: 0.2 A.U.s
Source for orbit data: Burnham's Celestial Handbook
As seen from B:
A would appear as magnitude -37.87

Component A:
Spectral class: B0
Luminosity Class: Ib
Apparent visual magnitude: +8.92 (increasing to +8.72)
Absolute visual magnitude: -2.80 (increasing to -3.00)
Visual luminosity: 1148 x Sol (increasing to 1380 x Sol)
Variable type: rotating ellipsoidal (rotating variable)
Period of variability: 5.59982 days
Color indices: B-V= -0.22
Mass: 25 x Sol
Source for mass: Burnham's Celestial Handbook
Diameter: 20 x Sol
Source for diameter: Burnham's Celestial Handbook
Comfort Zone (visual): 34 A.U.s
Orbital period in CZ: 39.4447 years
Tidal index in CZ: 0.000643
Angular size of star in sky in CZ: 0.314684 degrees

Component B:
Spectral class: X-rays only
Luminosity Class: black hole
Period of variability: 0.05 seconds
Mass: 12 x Sol
Source for mass: Burnham's Celestial Handbook
Diameter: 72 kilometers

Data for this star system were most recently updated on 9-October-1999.